The invention relates to a semiconductor device for mixing a received signal and a signal supplied by a local oscillator, for amplifying the result of this mixing process, and for rejecting a given frequency band. The semiconductor device comprises a dual gate field effect transistor with an intermediate ohmic island between two transistor halves of the dual gate field effect transistor. The source electrode is connected to ground, the received signal is applied to the first gate, and the signal supplied by the local oscillator is applied to either the first or the second gate of the dual gate field effect transistor. The resultant output signal is available at the drain electrode.
The invention relates to the field of semiconductor components, and more particularly to their application in the field of superfrequency satellite telecommunications.
The dual gate field effect transistor having an intermediate ohmic island is known from the prior art, especially from the U.S. Pat. No. 4,048,646 filed on Feb. 25, 1976 under Japanese priority on behalf of the assignee NIPPON ELECTRIC COMPANY, Limited
From publications by Van der Ziel and Takagi in I.E.E.E. Journal of Solid State Circuits (corresp). Vol. SC-4, June 1969, p. 170-172 in an article entitled "Improvement in the tetrode FET noise figure by neutralization and tuning", it is known to connect externally in cascade the common and intermediate electrode of an assembly of two FET transistors in order to reduce the noise level.
Such an assembly of two FET transistors connected in cascade is described, for example, in U.S. Pat. No. 3,986,060. More particularly in FIG. 9 of this patent, a device is illustrated in which the common and intermediate electrode is connected to ground through a resonant LC circuit.
It is well known from the prior art, for example, from an article published in I.E.E.E. Transactions on Microwave theory and techniques, Vol. MTT 23, No. 6, June 1975, entitled "Performance of dual-gate GaAS MESFET's as gain-controlled low-noise amplifiers and high-speed modulators," by C. A. LIECHTI, that a dual-gate transistor is equivalent to two single gate FET's connected in cascade.However, the circuit illustrated in FIG. 9 of U.S. Pat. No. 3,986,060 is limited to amplifiers, and does not relate to mixers.
Various ways of using a dual-gate field effect transistor, are known (e.g. as a mixer, modulator, power limiter, frequency multiplier, self-oscillating mixer etc.). The invention, however relates to a novel use of this known device in combination with inductive and capacitive elements to obtain a mixer-amplifier circuit suitable for rejecting a given frequency band.
It is known from the prior art to use a passive filter for rejecting bands by means of local elements and by way of example reference is made to the article "Monolithic low-noise amplifiers" by D. MAKI, R. ESFANDIARI and M. SIRACUSA published in MICROWAVES, pages 103-106, of October 1981. The disadvantage such a filter consists mainly in that losses on the order of 2 to 3 dB are introduced at the frequency of the signal, while band rejection is about 25 to 30 dB.
It is also known to use comparatively complex assemblies comprising several dual-gate transistors. By way of example, reference is made to the article "An X-band dual-gate MESFET Image rejection mixer", 1978, International Microwave Symposium Digest, pages 300-302.